As the average age of the United States population increases, so do the instances of aortic stenosis. An alternative approach to the conventional surgical replacement of the stenotic aortic valve involves the use of an apicoaortic conduit. In this approach, the native aortic valve is not removed, and a prosthetic valve is implanted in a parallel flow arrangement. A connection conduit (or tube) connects the apex of the heart to the descending aorta. Somewhere along this conduit, the prosthetic valve is interposed. Thus, blood leaves the heart through the apex and travels through the conduit (with valve) to the descending aorta.
Until recently, surgical procedures to implant an apicoaortic conduit have included a single, long incision, such as in the 6th intercostal space, to expose the heart and allow retraction of the lungs to expose the descending aorta. Recognizing the potential for broader scale use of the apicoaortic conduit for aortic valve replacement, some surgeons are now attempting to use smaller incisions and are requesting development of surgical tools for a minimally invasive procedure. As an initial attempt to make the procedure less invasive, some surgeons have recently performed the following procedure.
The patient is placed on the table in the supine position. Anesthesia is induced, and the patient is intubated with a double-lumen endotracheal tube, this facilitates one-lung ventilation and allows the surgeon to work within the left chest. The patient is positioned with the left side up (90 degrees). The pelvis is rotated about 45 degrees, such that the femoral vessels are accessible. An incision is made over the femoral vessels, and the common femoral artery and vein are dissected out. Heparin is administered. Pursestring sutures are placed in the femoral artery and vein. The artery is cannulated first, needle is inserted into the artery, and a guidewire is then inserted. Transesophageal echo is used to ascertain that the wire is in the descending aorta. Once this is confirmed, an arterial cannula is inserted over the wire, into the artery (Seldinger technique). The arterial cannula is typically 19 or 21 French. Once inserted, the pursestring sutures are snugged down over tourniquets. A similar procedure is followed for the femoral vein. The venous cannula is usually a few French larger than the arterial cannula. Once both vein and artery are cannulated, the cannulae are connected to the cardiopulmonary bypass, and the capability to initiate cardiopulmonary bypass at any time is present.
A 1 cm incision is made in approximately the 7th interspace in the posterior axillary line; the videoscope (10 mm diameter) is inserted, and the left chest contents viewed. The location of the apex of the heart is determined, and the light from the scope used to transilluminate the chest wall, which allows precise localization of the incision. The incision is then performed. It is essentially an anterior thoracotomy, typically in the 6th interspace. Recent incisions have been about 10 cm long, but are expected to become smaller and smaller with time. A retractor is inserted and the wound opened gently. A lung retractor is used to move the (deflated) left lung cephalad. The descending aorta is dissected free from surrounding soft tissue to prepare for the distal anastomosis. This dissection includes division of the inferior pulmonary ligament. A pledgeted suture is placed on the dome of the diaphragm and positioned to pull the diaphragm toward the feet (out of the way). The pericardium is incised about the apex of the heart, and the apex is freed up and clearly identified.
On the back table, the apicoaortic conduit is prepared, such as a 21 Freestyle valve sutured on the inflow opening to an 18-mm Medtronic apical connector and sutured on the outflow opening to a 20-mm Hemashield graft. The Dacron associated with the apical connector is pre-clotted with thrombin and cryoprecipitate. The assembly is brought to the field, and a measurement made from the apex of the heart to the descending aorta. The assembly is trimmed appropriately. A partial-occluding clamp is then placed on the descending aorta, and the aorta opened with a knife and scissors. The conduit (the end with the 20 mm Hemashield graft) is then sutured to the descending aorta using 4-0 prolene suture, in a running fashion. Once this is complete, the clamp is removed and the anastomosis checked for hemostasis. Blood is contained by the presence of the Freestyle aortic valve. The apical connector is placed on the apex, and a marker is used to trace the circular outline of the connector on the apex, in the planned location of insertion. Four large pledgeted sutures (mattress sutures) of 2-0 prolene are placed; one in each quadrant surrounding the marked circle. The sutures are then brought through the sewing ring of the apical connector. A stab wound is made in the apex in the center of the circle, and a tonsil clamp is used to poke a hole into the ventricle. Bypass may be initiated at this point, but some surgeons have developed crude manual techniques to avoid bypass entirely. A Foley catheter is inserted into the ventricle, and the balloon expanded. A cork borer is then used to cut out a plug from the apex. The connector is then parachuted down into position. A rotary motion is necessary to get the connector to seat in the hole. The four quadrant sutures are tied, and hemostasis is checked. If there is a concern regarding hemostasis, additional sutures are placed. The retractor is removed, chest tubes are placed, and the wound is closed.
Surgical tools developed specifically to implant the apicoaortic conduit are expected to provide the means for a much less invasive procedure. The procedure is expected to be performed with a series of smaller thoracotomy incisions between the ribs, such as immediately over the apex of the heart. In addition to avoiding the median sternotomy, development of appropriate surgical tools is expected to avoid the need for cardiopulmonary bypass, so that the procedure can be performed on a beating heart. The diseased aortic valve does not need to be exposed or excised. The stenotic aortic valve is left in place and continues to function at whatever level it remains capable of, and the apicoaortic conduit accommodates the balance of aortic output.
The major obstacle to widespread adoption of this superior configuration is the nearly complete lack of efficient devices to perform the procedure. Surgeons wishing to adopt the procedure must gather a collection of instruments from a variety of manufacturers. Often these instruments were created for quite different purposes, and the surgeon is forced to adapt them as required and manually manipulate them during a procedure.
U.S. Published Patent Application 2005/0149093 A1 (Pokorney) describes a device for implanting an apicoaortic conduit between the apex of the heart and the descending aorta. The device for cannulating the apex uses a piercing and dilating approach to avoid cutting a tissue plug. Substantial force may be required to cut and dilate a hole to place the conduit to its final position. The force may significantly deform the heart to prevent placement of the conduit or even harm internal heart structures.
U.S. Published Patent Application 2003/0130668 A1 (Nieman) describes ideas for remotely cannulating a body part, such as a heart. The method and apparatus are endoscopic, i.e. the instruments are mounted on the end of a long flexible member and inserted into the body through a trocar, i.e., a sharply pointed surgical instrument contained in a cannula. The endoscopic procedure appears complicated. After the device is placed at or near the apex of the heart, the surgeon or some other controller performs at least 13 separate steps to secure the cannula in the heart wall. Coordination of these steps with a user-friendly interface may be challenging. An attachment ring (which includes an apical ring and a locking stem) is sutured to the heart wall, and subsequently the cannula is connected to the attachment ring as a separate step. Because the procedure is endoscopic, imaging means (e.g., fluoroscopy) is used to place a balloon at the correct depth within the ventricle to provide occlusion.
The complex endoscopic procedure disclosed in Nieman appears to require that the cut tissue core be removed from the body prior to advancing the cannula to the heart wall. Further, Nieman appears to provide two mechanisms for placing the cannula in the heart wall. One such mechanism is to create a hole that is large enough to easily slide the cannula into the hole. This does not provide a tight fit between the cannula and cored heart wall to prevent blood loss from the cored heart wall and from the ventricle and relies entirely upon the sutured attachment ring to achieve hemostasis thus providing a period of time during which there could be great losses of blood. The second mechanism is to achieve a tight (interference) fit between the cannula and cored hole. However, such a tight fit requires substantial axial and torsional forces to be applied to the cannula. The flexible endoscopic instrument disclosed in Nieman may not provide such forces to be transmitted.
U.S. Pat. No. 7,077,801 (Haverich) discloses various approaches for implanting a conduit into the wall of a heart. As illustrated in FIG. 8A, Haverich shows a conduit on a cutter that has a “corkscrew driver” with a coil. The corkscrew is rotated to cause the cutter to penetrate through the myocardium. However, substantial axial force is required to cleanly penetrate the myocardium, and such force is not easily applied by a corkscrew. Further, the pointed tip of the corkscrew can damage other areas of the heart wall (e.g., the septum) while applying axial force and rotation. Haverich discloses a balloon used for hemostasis. However, the balloon is a separate instrument that cannot be combined with the corkscrew.
U.S. Pat. No. 6,726,648 (Kaplon) discloses a device similar to Haverich except that a trocar is used to penetrate the organ wall instead of a cutter with corkscrew. No tissue plug is formed with a trocar, but substantial force may be required. Use of a trocar makes it difficult to achieve hemostasis during a procedure on a beating heart. To address this, rigid conduit 18 is inserted through the connector 16 after the connector is implanted with the trocar and sewn into place. Connector 16 does not appear to penetrate the heart wall. Connector 16 has a built-in valve to prevent blood loss after the trocar is removed and until conduit 18 is inserted.
U.S. Pat. No. 6,942,672 (Heilman) discloses another device for implanting a conduit to the heart wall that uses a sealed enclosure to eliminate air and to prevent blood loss.